Patent GB-723540-A (GB)
Title: Improvements relating to fluid-operated automatic regulating or control apparatus
IPC: G05B6/05
Filed: 1951-09-28
Abstract: 723,540. Fluid-pressure servomotor-control systems. ELECTROFLO METERS CO., Ltd., and ENGLE, F. V. A. E. Dec. 23, 1952 [Sept. 28, 1951], No. 22710/51. Class 135. In fluid-operated automatic control apparatus for regulating a variable condition in which the fluid. pressure in an enclosed space is varied in dependence on the deviation of the variable condition from a predetermined value by means for measuring the actual value of the condition, means for introducing a derivative or " rate of change " action by enhancing the pressure variation in the enclosed space in functional relation with the rate of change of the deviation comprises a substantially freely movable pressure-responsive device such as a diaphragm or piston, which controls a valve device and which is in communication directly with, or is installed essentially within, the enclosed space, the pressure-responsive device and the valve device both being separate from the means which measure the value of the condition. In Fig. 1 compressible medium, such as air, is introduced into the enclosed space 3 through a restricted orifice 3a and passes to a relay or to a regulating device such as a valve or rheostat through a connection 3b. The pressure in the space 3 is regulated by a spring-loaded ball valve 2 operated through a link 1 by means (not shown) responsive to deviations in the variable condition from its predetermined value. The pressure in the space 3 is also regulated by a further spring-loaded ball valve 8 operated by a diaphragm or the like 7 which separates the space 3 from a chamber 4 connected to the space 3 by a passage 5 having adjustable throttling means and/or fixed throttling means 6. A rapid upward movement of the link 1 results in a sudden drop in the pressure in the space 3. Due to the throttling means 6, the pressure changes slowly in the chamber 4 and the valve 8 moves upwardly to increase still further the pressure drop in the chamber 3. Slow change in the position of the link 1 hardly effects the valve 8. In a modification, the ball valve 2 is replaced by flow-restricting device of the " flapper " -or baffle type and this is arranged in series with and on the outlet side of the valve 8. Fig. 3 shows a form suitable for use with liquids under pressure. The pressure in the enclosed space 16 is controlled primarily by a baffle 15 controlling a discharge nozzle 14 in accordance with deviations in the variable condition. The derivative action is introduced by a differential device comprising two spring-loaded pistons 18, 19. The piston 18 is open to the space 16 and provides the seat of a ball valve 20 loaded by a spring 20a which abuts the other piston 19. The annular chamber 21 below the piston 19 is connected to the space 16 through a passage 22 containing a throttling means 23. The valve seat responds rapidly to pressure changes in the space 16 whilst due to the throttling means the piston 19 and therefore the ball valve itself responds slowly. For slow pressure changes in the space 16 the relative positions of the ball valve and its seat remain unchanged. The arrangements in accordance with the invention may be used in conjunction with follow-up apparatus, or stabilizing means adapted to give proportional or integral control or both. Then the discharge nozzle may be carried by a piston actuated by differential pressures which are a function of the distance between the nozzle and the baffle so that the nozzle follows up the movements of the baffle. Specification 723,537 is referred to.